Nowadays, a printed circuit board (PCB) is an electronic component widely used in an electronic product of low current (such as a mobile phone, a digital camera, a PDA, a liquid crystal display, etc.) or an industrial apparatus of high electrical current (such as an electric control device, an electric transformation device, a cooling system, a multi-way socket, a socket of extension cord, etc.). According to the survey, there are still some disadvantages existing in the manufacture and operation of common commercially-available printed circuit boards. For example, a traditional photosensitive printed circuit board is described hereinafter, wherein a semi-finished product of the printed circuit board is provided with an insulation substrate which has a surface plated with a copper foil for electrical conduction, while the copper foil is coated with a photosensitive photoresist layer thereon. Generally, the semi-finished product of the printed circuit board is processed to form a finished product thereof by an operator according to the following steps:
(1) Designing a mask of circuit patterns;
(2) Attaching the mask of circuit patterns to the photosensitive photoresist layer on a surface of the semi-finished product;
(3) Processing the semi-finished product attached with the mask of circuit patterns by an exposure process;
(4) Removing the mask of circuit patterns;
(5) Immersing the semi-finished product in a development solution to carry out a development process, so as to remove exposed portions of the photosensitive photoresist layer of the semi-finished product;
(6) Immersing the semi-finished product in an etching solution (such as ferric chloride solution) to etch exposed portions of the copper foil uncovered by the photosensitive photoresist layer, so that the remaining copper foil on the semi-finished product forms circuit patterns;
(7) Washing to remove the remaining etching solution on the semi-finished product; and
(8) Drilling the semi-finished product to form connection holes for inserting other electronic components, such as resistors, capacitors, fuses and etc.
As described above, the manufacturing process of the printed circuit board comprises too many complicated steps which can not be simultaneously carried out, so that the manufacture efficiency of the printed circuit board can not be efficiently improved. In addition, because the copper foil on the printed circuit board for electrical conduction is formed on the insulation substrate by electroplating, the thickness of the copper foil is generally relatively thin. However, when the printed circuit board is applied to an industrial apparatus, the high electrical current used by the industrial equipment will cause the copper foil on the printed circuit board to generate high temperature. As a result, the printed circuit board will not be capable of loading the high electrical current and the high temperature generated by the high electrical current, resulting in damaging the printed circuit board or even causing accidental disasters. To solve the foregoing problems, there are two solutions. The first solution is to increase circuits (or jump wires) on the printed circuit board to evenly distribute the transmission pathway of the electric current. However, this solution will additionally cause the inconvenience of processing the printed circuit board and affect the appearance of the printed circuit board due to too many messy circuits. Furthermore, the second solution is to increase the thickness of the copper foil to prevent from causing the foregoing danger. However, the operator needs to use more precise electroplating equipments and more electroplating time to repeatedly execute the electroplating process for increasing the thickness of the copper foil, in order to control the copper foil to evenly and smoothly distribute on the insulation substrate. As a result, due to the second solution, the manufacture efficiency of the printed circuit board may be substantially lowered, while the manufacture cost of the printed circuit board may be increased. Thus, the competitiveness of manufacturers of the printed circuit board will be seriously affected. Therefore, it is important for related manufacturers of printed circuit boards to think how to improve the foregoing disadvantages existing in the manufacture and operation of the foregoing traditional printed circuit board.
It is therefore tried by the inventor to develop a circuit board capable of loading high electrical current to solve the problems existing in the manufacture and operation of the traditional printed circuit board, to simplify the manufacturing process of the circuit board, and to provide a capability of loading high electrical current.